A gas spring is normally pre-loaded with gas under high pressure, typically 60-160 bar. If the piston of the gas spring is accidentally broken away from the piston rod during use, the piston rod is free to accelerate in a piston rod guide on its way out of the gas spring.
U.S. Pat. No. 5,485,987 shows a gas spring where the piston rod seal is axially displaceable in order to open a normally closed radial bore through the cylinder, in order to permit escape of pressurized gas in case of the pressurized gas exceeding a predetermined pressure.
U.S. Pat. No. 5,454,455 shows a cylinder piston device where the piston, as it approaches the end of the cylinder, is arranged to abut against an indentation of the cylinder so as to be tilted or angled by the abutment in order to achieve a clamping effect which prevents expulsion of the piston rod and initiates a leak allowing pressurized fluid to escape.
A further gas spring is shown in DE-A1-24 57 938 in which pressurized fluid can be evacuated through controlled breakage of the cylinder and/or the piston rod at specially designed breaking points. In this type of arrangement, parts of the cylinder piston device are able to separate and become a high velocity projectile. DE-A1-42 16 573 shows a gas spring in which a guide is arranged to deform a piston rod seal in order to evacuate the pressurized gas from the gas spring if the pressure becomes too high.